In 2019, FISHBIO was hired to construct two custom weirs for the U.S. Fish & Wildlife Service’s Lahontan National Fish Hatchery Complex (LNFHC) in Garnerville, Nevada. The weirs are part of a reintroduction program to restore populations of Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) in the Truckee River watershed on Glen Alpine Creek, a tributary of Fallen Leaf Lake in El Dorado County, California. The portable rigid weirs allow juvenile Lahontan cutthroat trout to be captured for genetic testing, while allowing other smaller native species to pass through unhindered. The weirs feature both upstream and downstream fish traps that allow the USFWS to sort out nonnative trout to prevent hybridization with Lahontan cutthroats.
Lahontan cutthroat trout were reintroduced to Fallen Leaf Lake in 2002 by the LNFHC in an effort to reestablish a self-sustaining population in the Lake Tahoe Basin. However, nonnative rainbow trout (Oncorhynchus mykiss) and lake trout (Salvelinus namaycush) also live in Fallen Leaf Lake and can hinder restoration of Lahontan cutthroat trout through interbreeding and competition. Both lake-dwelling rainbow and Lahontan cutthroat spawn in upriver tributaries, and migrate downstream to larger bodies of water as juveniles. The weirs will be installed upstream of Fallen Leaf Lake on Glen Alpine Creek during the trout spawning and juvenile outmigration season (March to July) to monitor Lahontan cutthroat trout populations spawning in the creek.
FISHBIO constructed a custom rigid weir specially designed to withstand the “flashy” flows that often occur on Glen Alpine Creek. The portable rigid weir components consist of collapsible aluminum A-frames and removable picket panels that can withstand high flows, can be laid flat during in the event of high debris flows, and can be completely removed within a few hours. The entire weir assembly consisting of live boxes, picket panels, and A-frame supports can be easily moved by a few people and reassembled in alternate configurations to fit a different site on the stream. The weirs will help LNFHC biologists monitor Lahontan cutthroat trout reproduction and manage the reintroduction effort.